Chained Calculator in JavaScript

This is a very small yet complete example of a chain design pattern implementation in JavaScript. Please feel free to ask questions if the comments are not that descriptive.

var Calc = function (value) {
  /* for more security */
  var me = this; 

  /* chaning function to add  */
  this.add = function(x) {
    value += x;
    return me;
  }
  
  /* chaining function to multiply */
  this.multiply = function(x) {
    value *= x;
    return me;
  }
  
  /* chaining function to subtract */
  this.subtract = function(x) {
    value -= x;
    return me;
  }

  /* chaning function to divide  */
  this.divide = function(x) {
    value /= x;
    return me;
  }
  
  /* chaining function to give the result */
  this.equals = function(callback) {
    callback(value);
    return me;
  }

  /* nomal function to return the result
     and to finish the chanin.
  */
  this.end = function() {
    return value;
  }
}


/*

How to use the calculator

*/

var calc = new Calc(10)
  .add(20)
  .multiply(4)
  .equals(function (result) {
    console.log("= " + result);
  })
  .add(1).equals(function(result) {
    console.log(result);
  }).divide(3);


console.log("final result: " + calc.end());